It is common in the field of color measurement technology to measure color properties of items. Such measurements are usually done as a part of a quality control or manufacturing process to ensure that the color of items provided are consistent from one product batch to the next.
One approach to color measurement uses integrating spheres to measure the reflectance of color specimen. For example, the Datacolor 800 family of instruments manufactured by Datacolor Inc. of Lawrenceville N.J., are spectrophotometers that incorporate integrating sphere devices to measure the color properties of samples.
When using an integrating sphere, it is possible to measure a sample with or without the specular component of reflection included. Commonly, the specular component included (SCI) and specular component excluded (SCE) parameters are measured separately with the aid of a mechanical specular port cover or baffle, commonly called a SCE port. Efforts have been made to eliminate the need of moving the mechanical port cover and thus enable the measurement of SCI and SCE parameters simultaneously.
For example, in U.S. Pat. No. 6,424,413, titled “Multi-Channel Integrating Sphere”, to Weber et. al., herein incorporated by reference in its entirety, teaches a method of measuring multiple-channel information simultaneously, including SCI and SCE reflectances. However, the Weber patent includes drawbacks that prevent the ready adoption of such technology. Specifically, the ideal SCE port of an integrating sphere is usually fairly large relative to the rest of the integrating sphere. Likewise, the SCI effective area (that is the area of specular reflection) is also equally large. Commonly, and currently, the desire for a large SCE port and a large SCI effective area come into conflict. If both the SCE port and the SCI effective area are maximized and measurements are attempted to be made simultaneously, then the areas will overlap introducing error into the measurements.
As such, without mechanical baffles or port covers, SCI measurements can hardly be made simultaneously with SCE measurement. Furthermore, when designing the SCE port, it becomes difficult to determine how to weigh the desire for maximal port size against the other features (light leakage etc.) that are necessary design considerations to take into account when designing measurement devices in general and integrating spheres in particular. For example, those skilled in the art will appreciate that making the SCE port too big or too small will cause the measurement results to be erroneous. Another drawback of having a large SCE port is that it will impact the efficiency of the integrating sphere due to the light leakage from the SCE port. The bigger the SCE port is, the lower efficiency the integrating sphere will be.
Therefore, what is needed in the art is an integrating sphere having a SCE port sized and located such that the SCE port does not impact the SCI measurements. Furthermore, what is also needed is a SCE port having dimensions such that the SCE parameters can be properly measured at the same time as the SCI parameters.